Wang Yanfei, Hase William L, Song Kihyung
Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.
J Am Soc Mass Spectrom. 2003 Dec;14(12):1402-12. doi: 10.1016/j.jasms.2003.08.014.
A quantum mechanical and molecular mechanical (QM + MM) direct dynamics classical trajectory simulation is used to study energy transfer and fragmentation in the surface-induced dissociation (SID) of N-protonated diglycine, (gly)2H+. The peptide ion collides with the hydrogenated diamond [111] surface. The Austin Model 1 (AM1) semiempirical electronic structure theory is used for the (gly)2H+ intramolecular potential and molecular mechanical functions are used for the diamond surface potential and peptide/surface intermolecular potential. The simulations are performed at collision energies Ei of 30, 50, 70, and 100 eV and collision angle of 0 degrees (perpendicular to the surface). The percent energy transfer to the peptide ion is nearly independent of Ei, while energy transfer to the surface increases with increase in Ei. A smaller percent of the energy remains in peptide translation as Ei is increased. These trends in energy transfer are consistent with previous trajectory simulations of SID. At each Ei the most likely initial pathway leading to fragmentation is rupture of the +H3NCH2-CONHCH2COOH bond. Fragmentation occurs by two general mechanisms. One is the traditional Rice-Ramsperger-Kassel-Marcus (RRKM) model in which the peptide ion is activated by its collision with the surface, "bounces off", and then dissociates after undergoing intramolecular vibrational energy redistribution (IVR). The other mechanism is shattering in which the ion fragments as it collides with the surface. Shattering is the origin of the large increase in number of product channels with increase in Ei, i.e., 6 at 30 eV, but 59 at 100 eV. Shattering becomes the dominant dissociation mechanism at high Ei.
采用量子力学与分子力学相结合的直接动力学经典轨迹模拟方法，研究了N-质子化二甘氨酸（(gly)2H+）表面诱导解离（SID）过程中的能量转移和碎片化现象。肽离子与氢化金刚石[111]表面发生碰撞。采用奥斯汀模型1（AM1）半经验电子结构理论描述(gly)2H+的分子内势能，用分子力学函数描述金刚石表面势能和肽/表面分子间势能。模拟在碰撞能量Ei为30、50、70和100 eV以及碰撞角为0度（垂直于表面）的条件下进行。转移到肽离子上的能量百分比几乎与Ei无关，而转移到表面的能量随Ei的增加而增加。随着Ei的增加，留在肽平移中的能量百分比变小。这些能量转移趋势与之前SID的轨迹模拟结果一致。在每个Ei下，导致碎片化的最可能初始途径是+H3NCH2-CONHCH2COOH键的断裂。碎片化通过两种一般机制发生。一种是传统的赖斯-拉姆施泰格-卡塞尔-马库斯（RRKM）模型，其中肽离子通过与表面碰撞而被激活，“反弹”，然后在经历分子内振动能量重新分布（IVR）后解离。另一种机制是破碎，即离子在与表面碰撞时发生碎片化。破碎是随着Ei增加产物通道数量大幅增加的原因，即30 eV时为6个，但100 eV时为59个。在高Ei下，破碎成为主要的解离机制。
